The cyclization of 2-chlorosulfinylazetidinones with a Lewis acid-type Friedel-Crafts catalyst, a Bronsted proton acid-type Friedel-Crafts catalyst, or a metathetic cation-forming agent is described by Kukolja in U.S. Pat. No. 4,052,387. The cyclization results in the formation of a 3-exomethylenecepham sulfoxide ester. The process is useful in an overall two-step process for converting penicillin sulfoxide esters to the 3-exomethylenecepham ester sulfoxides which proceeds through the intermediate 2-chlorosulfinylazetidinones. The two-step process is illustrated in the following generalized reaction scheme. ##STR1##
The preparation of 2-chlorosulfinylazetidinones and their use in the two-step process is described by Chou in U.S. Pat. No. 4,075,203. In co-pending application Ser. No. 960,347, filed this even date, there is described an improved process for the preparation of the 2-chlorosulfinylazetidinone intermediates which comprises the use of an insoluble poly(4-vinylpyridine)-divinylbenzene cross-linked co-polymer as the hydrogen chloride-binding agent, rather than the epoxide or epoxide-calcium oxide combinations as taught in U.S. Pat. No. 4,075,203.
The 2-chlorosulfinylazetidinone is employed as the intermediate in the Friedel-Crafts catalyzed cyclization to the 3-exomethylenecepham sulfoxide as shown above.
Accordingly, the above-described two-step process represents a method for preparing a cephalosporin-type compound from a penicillin-type compound which differs from the process described by Morin and Jackson in U.S. Pat. No. 3,275,626, wherein the acid catalyzed heat rearrangement of a penicillin sulfoxide ester to a desacetoxycephalosporin ester is described.